1. Field of the Invention
This invention relates to lead-free projectiles fired from rifles, pistols and shotguns. More particularly, a projectile having an essentially pure tin core exhibits performance characteristics similar to lead without presenting the environmental hazards of lead.
2. Description of Related Art
Most bullets fired from pistols and rifles have a lead base alloy core, meaning the core is either entirely or more than 50%, by weight, lead. The environmental hazards of lead are well known. Lead containing bullets fired into the ground are suspected to cause ground water pollution through leaching. Another problem facing shooters is that when a bullet having exposed lead is fired, a lead-containing dust from the projectile is emitted. These lead fumes are toxic and, if inhaled, present a hazard to the shooter. An additional hazard, lead is leached into ground water from unrecovered bullets.
Many alternatives to a lead core bullet have been disclosed. U.S. Pat. No. 5,399,187 to Mravic et al. discloses a sintered bullet core formed from a combination of a material having a density less than lead and a second material having a density greater than lead. One disclosed combination is a mixture of tin and tungsten.
U.S. Pat. No. 5,500,183 to Noordegraaf et al. discloses a non-jacketed bullet formed from a tin base alloy that contains as an alloy addition one or more of copper, antimony, bismuth and zinc. The bullet has a hardness on the order of at least 14 Brinell. Eutinal, a zinc-aluminum-magnesium alloy, is added to the tin base alloy to enhance ductility.
U.S. Pat. No. 5,679,920 to Hallis et al. discloses jacketed bullets having a core formed from twisted and swaged strands of zinc wire.
GB 2,279,440 discloses a projectile, pellet or bullet, for an air, gas or spring gun. The projectile may be formed from zinc, zinc alloy, copper, tin, bismuth or brass provided that the projectile forming metal is harder than lead or a lead alloy, but soft enough not to score the barrel bore.
While the projectiles disclosed in the above patents are lead-free, the cores of these projectiles are harder than lead causing the projectiles to have an unacceptable degree of ricochet. In addition, zinc containing cores may also pose an environmental hazard. Zinc fumes are noted in the ASM Handbook, Volume 2, as suspected to have a detrimental effect on health.
There remains, therefore, a need for a projectile that is both lead-free and zinc-free and has performance characteristics similar to that of a projectile with a lead base core. Among the performance characteristics of lead that enhance bullet performance are malleability, density and low cost.
Accordingly, it is an object of the invention to provide a lead-free projectile with upset characteristics similar to that of lead without the environmental hazards of lead. It is a feature of the invention that, in one embodiment, the projectile has an essentially pure tin core surrounded by a copper alloy jacket. In alternative embodiments, the essentially pure tin core is not jacketed.
Among the advantages of the invention are that the projectile has upset characteristics similar to that of lead and, by being lead-free, has a reduced impact on the environment. The projectiles are suitable for all types of bullets, jacketed or not, including pistol and rifle. The projectiles of the invention are useful for soft point, partition, and hollow point bullets, as well as other bullet configurations. The projectiles are also useful as slugs for shotguns.
In accordance with the invention, there is provided a lead-free projectile. The lead-free projectile has a metallic jacket with an outer surface defining an aerodynamic projectile and an inner surface defining at least one cavity. The at least one cavity is filled with essentially pure tin that has a yield strength that is equal to or less than 11 MPa.
The above stated objects, features and advantages will become more apparent from the specification and drawings that follow.